Climate change&#8208;driven shifts in species ranges are ongoing and expected to increase. However, life&#8208;history traits may interact with climate to influence species ranges, potentially accelerating or slowing range shifts in response to climate change. Tropical mangroves have expanded their ranges poleward in the last three decades. Here, we report on a shift at the range edge in life&#8208;history traits related to reproduction and dispersal. With a common garden experiment and field observations, we show that Rhizophora&nbsp;mangle individuals from northern populations reproduce at a younger age than those from southern populations. In a common garden at the northern range limit, 38% of individuals from the northernmost population were reproductive by age 2, but less than 10% of individuals from the southernmost population were reproductive by the same age, with intermediate amounts of reproduction from intermediate latitudes. Field observations show a similar pattern of younger reproductive individuals toward the northern range limit. We also demonstrate a shift toward larger propagule size in populations at the leading range edge, which may aid seedling growth. The substantial increase in precocious reproduction at the leading edge of the R.&nbsp;mangle range could accelerate population growth and hasten the expansion of mangroves into salt marshes.

ece32270-fig-0003: Rhizophora mangle propagule length increases with latitude in sites spanning the Atlantic coast of Florida. The 30 largest propagules were collected from each site, with no more than three propagules from the same individual. Points are means ± SE for each site. The fitted line is y = e^(−0.622 + 0.142x) (r2 = 0.878).

Mentions:
We sampled R. mangle in naturally occurring populations and found that there is a significant difference among sites in the age at which individuals reach reproductive maturity (log‐rank test, X2 = 9.5, df = 2, P = 0.008). Individuals from pure mangrove sites south of the ecotone are much less likely to be reproductive by age 6 than individuals in the middle of the ecotone or at the northern range edge (Fig. 3). Additionally, mangrove propagule size changes along the mangrove–salt marsh ecotone, with R. mangle propagules approaching larger sizes with increasing latitude. Mean propagule length was related linearly to latitude on a log scale (Fig. 4, F1,5 = 36, P = 0.002).

ece32270-fig-0003: Rhizophora mangle propagule length increases with latitude in sites spanning the Atlantic coast of Florida. The 30 largest propagules were collected from each site, with no more than three propagules from the same individual. Points are means ± SE for each site. The fitted line is y = e^(−0.622 + 0.142x) (r2 = 0.878).

Mentions:
We sampled R. mangle in naturally occurring populations and found that there is a significant difference among sites in the age at which individuals reach reproductive maturity (log‐rank test, X2 = 9.5, df = 2, P = 0.008). Individuals from pure mangrove sites south of the ecotone are much less likely to be reproductive by age 6 than individuals in the middle of the ecotone or at the northern range edge (Fig. 3). Additionally, mangrove propagule size changes along the mangrove–salt marsh ecotone, with R. mangle propagules approaching larger sizes with increasing latitude. Mean propagule length was related linearly to latitude on a log scale (Fig. 4, F1,5 = 36, P = 0.002).

Climate change&#8208;driven shifts in species ranges are ongoing and expected to increase. However, life&#8208;history traits may interact with climate to influence species ranges, potentially accelerating or slowing range shifts in response to climate change. Tropical mangroves have expanded their ranges poleward in the last three decades. Here, we report on a shift at the range edge in life&#8208;history traits related to reproduction and dispersal. With a common garden experiment and field observations, we show that Rhizophora&nbsp;mangle individuals from northern populations reproduce at a younger age than those from southern populations. In a common garden at the northern range limit, 38% of individuals from the northernmost population were reproductive by age 2, but less than 10% of individuals from the southernmost population were reproductive by the same age, with intermediate amounts of reproduction from intermediate latitudes. Field observations show a similar pattern of younger reproductive individuals toward the northern range limit. We also demonstrate a shift toward larger propagule size in populations at the leading range edge, which may aid seedling growth. The substantial increase in precocious reproduction at the leading edge of the R.&nbsp;mangle range could accelerate population growth and hasten the expansion of mangroves into salt marshes.